南京智热节能科技有限公司

Heat exchanger (heat exchanger) is a device that transfers part of the heat of the hot fluid to the cold fluid, also known as the heat exchanger. Heat exchanger plays an important role in chemical, petroleum, power, food and many other industrial production. It can be used as heater, cooler, condenser, evaporator and reboiler in chemical production.

Development

Heat exchanger is a kind of different temperature between two or more than two kinds of fluid to achieve the heat transfer between the material energy-saving equipment, is to make the heat from the higher temperature of the fluid to the lower temperature of the fluid, so that the fluid temperature to meet the process requirements, to meet the needs of process conditions, but also to improve the energy efficiency of one of the main equipment.

Heat exchanger industry involves HVAC, pressure vessels, water treatment equipment, chemical, petroleum and other nearly 30 kinds of industries, forming an industrial chain with each other. Data show that the market size of China's heat exchanger industry in 2010 was about 50 billion yuan, mainly concentrated in petroleum, chemical industry, metallurgy, electric power, shipbuilding, central heating, refrigeration and air conditioning, machinery, food, pharmaceutical and other fields.

Among them, the petrochemical industry is still the largest heat exchanger industry market, the market size of 15 billion yuan;

The market size of heat exchangers in the field of electric power metallurgy is about 8 billion yuan;

The market size of the ship industry heat exchanger is above 4 billion yuan;

The market size of mechanical industry heat exchanger is about 4 billion yuan;

The market size of heat exchanger in central heating industry exceeds 3 billion yuan;

The food industry also has a market of nearly 3 billion yuan.

In addition, aerospace vehicles, semiconductor devices, nuclear power regular islands, nuclear islands, wind turbines, solar photovoltaic power generation, polysilicon production and other fields require a large number of professional heat exchangers. These markets have a scale of about 13 billion yuan.

The domestic heat exchanger industry has made remarkable achievements in energy saving and efficiency enhancement, improving heat transfer efficiency, reducing heat transfer area, reducing pressure drop, and improving the thermal intensity of the device. Based on the steady growth of demand for heat exchangers in petroleum, chemical, electric power, metallurgy, shipbuilding, machinery, food, pharmaceutical and other industries, China's heat exchanger industry will maintain steady growth in the future. From 2011 to 2020, China's heat exchanger industry will maintain an average annual growth rate of about 10-15%, and the scale of China's heat exchanger industry is expected to reach 150 billion billion yuan by 2020.

Classification

It is suitable for heat exchangers with different media, different working conditions, different temperatures and different pressures, and the structure type is also different. The specific classification of heat exchangers is as follows:

Classification of 1. according to heat transfer principle

(I) between the wall heat exchanger between the wall heat exchanger is different temperature of two kinds of fluid flow in the space separated by the wall, through the wall of heat conduction and fluid convection on the wall surface, heat exchange between the two fluids. There are shell-and-tube heat exchangers, sleeve and other types of heat exchangers. The recuperative heat exchanger is the most widely used heat exchanger.

(II) regenerative heat exchanger The regenerative heat exchanger transfers heat from a high temperature fluid to a low temperature fluid through a heat storage body composed of a solid substance. The heat medium first reaches a certain temperature by heating the solid substance, and then the cold medium passes through the solid substance. The substance is heated to achieve the purpose of heat transfer. The regenerative heat exchanger has rotary type, valve switching type and so on.

(III) fluid connection indirect heat exchanger fluid connection indirect heat exchanger is a heat exchanger in which two surface heat exchangers are connected by a heat carrier circulating therein. The heat carrier circulates between the high temperature fluid heat exchanger and the low temperature fluid, receives heat in the high temperature fluid, and releases heat to the low temperature fluid in the low temperature fluid heat exchanger.

(IV) direct contact heat exchanger is also known as hybrid heat exchanger, this heat exchanger is two kinds of fluid direct contact, mixed with each other for heat exchange equipment such as cold water tower, gas condenser and so on.

The (V) compound heat exchanger has both steam-water surface indirect heat exchange and water-water direct mixed flow heat exchange equipment. Compared with the steam-water surface indirect heat exchange, it has higher heat exchange efficiency; compared with the steam-water direct mixed heat exchange, it has higher stability and lower unit noise.

Classification of 2. by use

(I) heater The heater heats the fluid to the necessary temperature, but there is no phase change in the heated fluid.

(II) preheater preheater preheats the fluid to provide standard process parameters for process operations.

(III) Superheater Superheater is used to heat a fluid (process gas or steam) to a superheated state.

(IV) evaporator evaporator is used to heat the fluid to reach a temperature above the boiling point to evaporate the fluid, generally with a phase change.

3. classified by structure

Can be divided into: floating head heat exchanger, fixed tube plate heat exchanger, U tube plate heat exchanger, plate heat exchanger, etc.

heat exchange mode

Inbound wall type

01 Jacketed heat exchanger

This heat exchanger is made by installing a jacket on the outer wall of the container, and its structure is simple; but its heating surface is limited by the wall of the container, and the heat transfer coefficient is not high. In order to improve the heat transfer coefficient and make the liquid in the kettle evenly heated, a stirrer can be installed in the kettle. When cooling water or a heating agent without phase change is introduced into the jacket, a spiral partition or other measures to increase turbulence can also be set in the jacket to increase the heat supply coefficient on one side of the jacket. In order to supplement the shortage of heat transfer surface, the coil tube can also be installed inside the kettle. Jacketed heat exchanger is widely used for heating and cooling of the reaction process.

02 immersed coil heat exchanger

This kind of heat exchanger is to bend the metal tube into various shapes suitable for the container and immerse it in the liquid in the container. The advantages of the snake tube heat exchanger are simple structure, can withstand high pressure, and can be made of corrosion-resistant materials.; Its disadvantage is that the degree of turbulence of the liquid in the container is low, and the heat coefficient outside the tube is small. In order to improve the heat transfer coefficient, the container can be equipped with a stirrer.

03 Spray heat exchanger

This heat exchanger is a row of heat exchange tubes fixed on the steel frame, hot fluid flow in the tube, cooling water from the top of the spray device evenly under the shower, it is also known as the spray cooler. The outside of the tube of the spray heat exchanger is a layer of liquid film with a high degree of turbulence, and the heat coefficient outside the tube is much larger than that of the immersion type. In addition, most of this heat exchanger is placed in the air circulation, and the evaporation of the cooling water also takes away part of the heat, which can reduce the temperature of the cooling water and increase the heat transfer driving force. Therefore, compared with the immersion type, the heat transfer effect of the spray type heat exchanger is greatly improved.

Sleeve heat exchanger Sleeve heat exchanger is a concentric sleeve made of straight tubes with different diameters and connected by U-shaped elbows. In this heat exchanger, one fluid goes through the tube and the other fluid goes through the annulus, both of which can obtain a higher flow rate, so the heat transfer coefficient is larger. In addition, in a double-pipe heat exchanger, the two fluids can be purely countercurrent, and the log-averaged driving force is large. The casing heat exchanger is simple in structure, can withstand high pressure, and is convenient to use (the number of pipe sections can be increased or decreased as needed). Especially because the casing heat exchanger has the advantages of large heat transfer coefficient, large heat transfer driving force and strong ability to withstand high pressure.

04 plate heat exchanger

The most typical recuperator, it has a long history of industrial applications, and still in all heat exchangers dominate. The main structure is composed of heat exchange plates and rubber strips between the plates. Long-term dominant in the market, but its large volume, low heat exchange efficiency, the replacement of the rubber strip is expensive (the replacement cost of the rubber strip is about 1/3-1/2 of the whole process). Mainly used in liquid-liquid heat exchange between the industry is often called water heat exchange, the heat exchange efficiency of 5000w/m2.K.

In order to improve the heat transfer coefficient of the fluid outside the tube, a certain number of transverse baffle plates are usually installed in the housing. The baffle plate can not only prevent the fluid short circuit and increase the fluid velocity, but also force the fluid to cross flow through the tube bundle many times according to the specified path, so that the degree of turbulence is greatly increased. The commonly used baffles are rounded and disc-shaped, the former is more widely used..

Due to the launch of China's new version of GMP, plate heat exchange will gradually withdraw from food, beverage, pharmaceutical and other high-level health industries.

05 shell and tube heat exchanger

Shell-and-tube heat exchanger (also known as tubular) is a shell-and-tube heat exchanger mainly composed of shell, tube bundle, tube sheet and head. The shell is mostly round, with parallel tube bundle or spiral tube inside, and both ends of the tube bundle are fixed on the tube sheet.

In the shell and tube heat exchanger for heat exchange of two kinds of fluid, a flow in the tube, its stroke is called tube side; a flow in the tube, its stroke is called shell side. The wall of the tube bundle is the heat transfer surface. There are different types of pipes. The process is generally 16mm to 20mm or 25mm in diameter, and the thickness of the pipe wall is generally 1mm,1.5mm,2mm and 2.5mm. Imported heat exchangers, with a minimum diameter of 8mm and a wall thickness of only 0.6mm mm, have greatly improved the heat exchange efficiency and have been vigorously promoted in the domestic market since 2012.

Shell and tube heat exchanger, spiral tube bundle design, can maximize the increase of turbulence effect, increase heat transfer efficiency. The asymmetric design of the internal shell and tube layer can reach a maximum of 4.6 times. This asymmetric design determines its wide application in the field of steam-water heat exchange. The maximum heat exchange efficiency can reach 14000w/m2.k, which greatly improves production efficiency and saves costs. At the same time, because the shell and tube heat exchangers are mostly metal structures, with the introduction of the new version of GMP in China, the heat exchanger with stainless steel 316L as the main body will become a must for the beverage, food, and pharmaceutical industries.

06 Double tube plate heat exchanger

Also known as P-type heat exchanger, the heat exchanger is in the shell and tube heat exchanger at both ends plus a tube plate, can effectively prevent leakage caused by pollution. There are few domestic brands in the market and their prices are expensive, generally above 100000 yuan, and imports can reach hundreds of thousands, which is in line with the new GMP regulations. Although the price is expensive, it determines its broad market.

Hybrid

The hybrid heat exchanger relies on direct contact of cold and hot fluids for heat transfer. This heat transfer method avoids the thermal resistance of the heat transfer partition wall and the dirt on both sides. As long as the contact between the fluids is good, there is a larger Heat transfer rate.

Therefore, where the fluids are allowed to mix with each other, hybrid heat exchangers can be used, such as gas washing and cooling, cooling of circulating water, mixed heating between steam and water, condensation of steam, etc. Its application throughout the chemical and metallurgical enterprises, power engineering, air conditioning engineering and many other production sectors. According to different applications, hybrid heat exchangers can be divided into the following types:

(1) cooling tower (or cold water tower) in this kind of equipment, with natural ventilation or mechanical ventilation method, the production has increased the temperature of the water after cooling and recycling, in order to improve the economic efficiency of the system. For example, circulating water in thermal power plants or nuclear power plants, cooling water in synthetic ammonia production, etc., are recycled after cooling by water cooling towers. This method has been widely used in practical projects.

(2) Gas scrubbing tower (or scrubbing tower) In industry, this equipment is used to scrub gas for various purposes, such as absorbing certain components of the gas mixture with liquid, removing dust from the gas, humidifying or drying the gas, etc. However, its most extensive use is for cooling gases, and the liquid used for cooling is mostly water. The spray room widely used in air conditioning engineering can be considered as a special form of it. The spray chamber can not only cool the air like a gas scrubber, but also heat it. However, it also has the disadvantages of high water quality requirements, large footprint, and high water pump energy consumption: therefore, in general buildings, the spray room is not often used or only used as humidification equipment. However, in order to adjust the humidity as the main purpose of the textile mills, cigarette factories, etc. are still widely used!

(3) Jet heat exchanger In this equipment, the higher pressure fluid is sprayed from the nozzle to form a high speed. The low pressure fluid is introduced into the mixing chamber to directly contact with the jet for heat transfer, and enter the diffusion tube together. After reaching the same pressure and temperature at the outlet of the diffusion tube, it is sent to the user.

(4) Hybrid Condenser This equipment generally condenses steam by directly contacting water with steam.

heat storage type

The regenerative heat exchanger is used for the equipment of regenerative heat exchange. It is filled with solid filler to store heat. Generally, refractory bricks are used to build fire lattices (sometimes with metal corrugated belts, etc.). Heat exchange is carried out in two stages. In the first stage, the hot gas passes through the fire lattice, transferring heat to the fire lattice and storing it. In the second stage, the cold gas passes through the fire lattice and receives the heat stored in the fire lattice to be heated. These two phases alternate. Usually two regenerators are used alternately, that is, when the hot gas enters one, the cold gas enters the other. Commonly used in the metallurgical industry, such as the regenerator of open-hearth steelmaking. It is also used in the chemical industry, such as air preheaters or combustion chambers in gas furnaces, and regenerative cracking furnaces in artificial oil plants. Thermal heat exchangers are generally used for occasions where the requirements for medium mixing are relatively low.

A Ceramic

Ceramic heat exchanger is a new type of tube type high temperature heat recovery device, the main component is silicon carbide, can be widely used in metallurgy, machinery, building materials, chemical and other industries, direct recovery of various industrial kiln emissions of 850-1400 ℃ high temperature flue gas waste heat, in order to obtain high temperature combustion air or process gas.

B Ceramic heat exchanger

The heat exchange element material of this device is a new type of silicon carbide engineering ceramic, which has excellent performance of high temperature resistance and thermal shock resistance. It is air-cooled from 1000 ℃ to room temperature and repeated more than 50 times without cracks. The thermal conductivity is equivalent to that of stainless steel. It has good corrosion resistance in oxidizing and acidic media. The problem of thermal compensation and gas sealing is solved successfully in structure. The device has high heat transfer efficiency and significant energy saving effect, which is used

Preheating combustion air or heating process gas in certain processes can save primary energy, fuel saving rate can reach 30% ~ 55%, and can strengthen the process and significantly improve production capacity.

The production process of ceramic heat exchanger is basically the same as that of kiln furniture, and the thermal conductivity and oxidation resistance are the main application properties of the material. Its principle is to place the ceramic heat exchanger near the flue outlet and at a higher temperature without adding cold air and high temperature protection. When the kiln temperature is 1250-1450 ℃, the temperature at the flue outlet should be 1000-1300 ℃, and the waste heat recovered by the ceramic heat exchanger can reach 450-750 ℃. The recovered hot air is sent into the kiln to form a mixed gas for combustion, thus directly reducing the production cost and increasing the economic benefits. Ceramic heat exchanger has been well developed under the limitation of the use of metal heat exchanger, because it solves the problems of corrosion resistance and high temperature resistance. Its main advantages are: good thermal conductivity, high temperature strength, oxidation resistance and thermal shock resistance. Long life, small maintenance, reliable and stable performance, easy to operate.

floating head type

1 Design requirements

With the development of economy, various types and types of heat exchangers are developing rapidly, and heat exchangers with new structures and new materials are emerging. In order to meet the needs of development, China has established standards for certain types of heat exchangers and formed a series. Perfect heat exchanger in the design or selection should meet the following basic requirements:

(1) Reasonably achieve the specified process conditions.

(2) The structure is safe and reliable.

(3) Easy to manufacture, install, operate and maintain.

(4) Economically reasonable.

One end of the floating head heat exchanger tube sheet and shell fixed, and the other end of the tube sheet can be free floating in the shell, shell and tube bundle on the expansion is free, so when the temperature difference between the two media is large, the tube bundle and shell does not produce temperature difference stress. The floating head end is designed as a detachable structure, so that the tube bundle can be easily inserted or withdrawn from the housing. (Can also be designed to be non-removable). This provides convenience for maintenance and cleaning. However, the structure of the heat exchanger is complex, and the small cover at the floating end cannot know the leakage during operation.

Therefore, special attention should be paid to its sealing during installation. The structure of the floating head part of the floating head heat exchanger can be designed into various forms according to different requirements. In addition to the free movement of the tube bundle in the equipment, the convenience of maintenance, installation and cleaning of the floating head part must also be considered. The outer diameter Do of the floating head tube plate must be considered in the design. The outer diameter should be less than the shell inner diameter Di, generally recommend the gap between the floating head tube plate and the shell inner wall b1 = 3~5mm. In this way, when the hook ring of the floating head is removed, the tube bundle can be extracted from the shell. In order to facilitate maintenance, cleaning. The floating head cover can only be assembled after the tube bundle is installed, so the necessary space for the floating head cover during assembly should be considered in the design. The hook ring plays an important role in ensuring the sealing of the floating head end and preventing the leakage of the series between the media.

With the development of the design and manufacturing technology of the heat exchanger, as well as the accumulation of long-term experience, the structure of the hook and loop has also been improved and perfected. The hook ring is generally a split structure, which requires reliable sealing, simple and compact structure, easy to manufacture and easy to disassemble. With its high reliability and wide adaptability, floating head heat exchanger has accumulated rich experience in the process of long-term use. Despite the challenges of emerging new heat exchangers, they in turn continue to promote their own development. So far, it is still dominant in various heat exchangers.

2 Advantages and disadvantages

A: Advantages

(1) The tube bundle can be drawn out to facilitate cleaning of the tube and shell.

(2) The temperature difference between the media is not limited.

(3) It can work under high temperature and high pressure, generally the temperature is less than or equal to 450 degrees, and the pressure is less than or equal to 6.4 MPa.

(4) can be used for scaling more serious occasions.

(5) can be used for pipe corrosion occasions.

B: Disadvantages

(1) Small floating head is prone to internal leakage.

(2) The consumption of metal materials is large and the cost is 20% higher.

(3) the structure is complex.

3 Manufacturing process

Select the manufacturing materials and grades of heat exchange equipment, test the chemical composition of the materials, and after the mechanical properties are qualified, the steel plate is orthopedic, including manual orthopedic, mechanical orthopedic and flame orthopedic.

Material preparation-marking-cutting-edge processing (flaw detection)-forming-assembly-welding-welding quality inspection-assembly welding-pressure test quality inspection Chemical equipment not only inspects raw materials before manufacturing, And check at any time during the manufacturing process.

Precautions

1. Keep the pipe network clean. Whether it is before or after the work is completed, the pipe network must be cleaned. The purpose of this is to avoid the phenomenon of heat exchanger blockage. Also pay attention to the cleaning of the decontamination device and the filter in time, so that the whole work can be completed smoothly.

2. Strictly control softened water. It is very important for water quality control. Under the premise of softening water quality treatment, the water quality in the system and softening tank should be carefully checked first, and the injection treatment can be carried out after being determined to be qualified.

3. New system test. For some new systems, can not immediately be used alternately with the heat exchanger, the first need to run the new system in a specified period of time, so that it has a mode of operation, then the heat exchanger can be incorporated into the system to use, the purpose of doing so is entirely to avoid the impurities in the pipe network damage heat exchanger equipment.

Industry Status

Heat exchanger in petroleum, chemical, light industry, pharmaceutical, energy and other industrial production, often used to heat the low temperature fluid or the high temperature fluid cooling, the liquid vaporization into steam or steam condensation into liquid. The heat exchanger is not only a unit equipment, such as heater, cooler and condenser, but also an integral part of a process equipment, such as the heat exchanger in the ammonia synthesis tower. Heat exchanger is an important unit equipment in chemical production. According to statistics, the tonnage of heat exchanger accounts for about 20% of the whole process equipment, and even as high as 30%. Its importance can be imagined.

01 Shell and tube type

Shell and tube heat exchanger is a large quantity and a wide variety of products, the urgent need for new wear-resistant, corrosion-resistant, high-strength materials. China in the development of stainless steel copper alloy composite materials, aluminum magnesium alloy and silicon carbide and other non-metallic materials have different degrees of progress, especially in the rapid development of titanium. Titanium has good corrosion resistance to seawater, chlor-alkali, acetic acid, etc. If heat transfer is enhanced, the effect will be better. Some manufacturing units have better mastered the processing and manufacturing technology of titanium materials. For the spraying of materials, China has imported production lines from abroad.

Aluminum magnesium alloy has high corrosion resistance and thermal conductivity, the price is cheaper than titanium, should be noted. Remarkable achievements have been made in domestic research on improving the performance of heat exchangers, improving heat transfer efficiency, reducing heat transfer area, reducing pressure drop, and improving the thermal strength of the device. The extensive use of heat exchangers effectively improves the utilization rate of energy, reduces the cost of enterprises and improves the efficiency.

02 Vortex Hot Film Heat Exchanger

The vortex hot film heat exchanger adopts the latest vortex hot film heat transfer technology, which increases the heat transfer effect by changing the fluid motion state. When the medium passes through the surface of the vortex tube, the surface of the tube will be washed strongly, thereby improving the heat transfer efficiency. Up to 10000W/m2 ℃.

This structure realizes the functions of corrosion resistance, high temperature resistance, high pressure resistance and anti-scaling. The fluid channel of other types of heat exchangers is in the form of fixed direction flow, which forms a winding flow on the surface of the heat exchange tube, and the convective heat transfer coefficient is reduced. The biggest characteristic of vortex heat exchanger is the unity of economy and safety.

Considering the flow relationship between the heat exchange tubes and between the heat exchange tubes and the shell, the baffle plate is no longer used to force out the turbulence, but the alternating vortex flow is naturally induced between the heat exchange tubes, and the vibration strength is maintained under the premise of ensuring that the heat exchange tubes do not rub against each other. The rigidity and flexibility of the heat exchange tubes are well configured and will not collide with each other, which not only overcomes the problem of damage caused by collision between floating coil heat exchangers, but also avoids the problem of fouling of ordinary shell and tube heat exchangers.

A Performance characteristics

(1) High efficiency and energy saving, the heat transfer coefficient of the heat exchanger is 6000-8000W/m2.0C.

(2) All stainless steel production, long service life, up to 20 years.

(3) The laminar flow is changed to turbulent flow, which improves the heat exchange efficiency and reduces the thermal resistance.

(4) fast heat exchange, high temperature resistance (400 ℃), high pressure resistance (2.5Mpa).

(5) Compact structure, small footprint, light weight, convenient installation, and saving civil engineering investment.

(6) flexible design, complete specifications, practical pertinence, saving money.

(7) a wide range of application conditions, suitable for large pressure, temperature range and a variety of media heat exchange.

(8) Low maintenance cost, easy operation, long cleaning cycle and convenient cleaning.

(9) the use of nano thermal film technology, significantly increase the heat transfer coefficient.

(10) It has a wide range of applications and can be widely used in thermal power, factories and mines, petrochemicals, urban central heating, food and medicine, energy electronics, mechanical light industry and other fields.

new type

1 Pneumatic spraying

Russia has proposed an advanced method, the pneumatic spraying method, to improve the performance of finned surfaces. The essence of this is the use of high-speed cold or slightly warmed particulate-containing fluid to spray powder particles on the fin surface. With this method, not only metals but also alloys and ceramics (metal-ceramic mixtures) can be sprayed to obtain surfaces of various properties. Often in practice, the contact resistance of the bottom surface of the fin is one of the factors that limit the addition of fins to the tube. An experimental study was carried out in order to evaluate the finned tube heat exchanger elements. The experiment was conducted by spraying ac-aluminum on the fin surface and adding 24a white electric furnace aluminum oxide. The contact resistance of the bottom surface of the fin can be evaluated by collating the data obtained from the test.

Comparing the efficiency of the studied fins with the calculated data, it is concluded that the contact resistance of the bottom surface of the pneumatic spray fin has no substantial effect on the efficiency.

In order to confirm this, the metallographic structure analysis of the transition zone between the base (tube) and the surface (fin) was carried out. The analysis of the transition zone specimen shows that there are no non-tight microcracks on the entire length of the connection boundary. Therefore, the pneumatic spraying method promotes the formation of the branch boundary between the surface and the basic interaction, and can promote the penetration of the powder particles into the matrix, which shows that the adhesion strength is high, the physical contact and the formation of the metal chain. Therefore, the pneumatic spraying method can not only be used for molding, but also can be used to fix the fins manufactured by the ordinary method on the surface of the heat exchanger tube, and can also be used to supplement and reinforce the bottom surface of the ordinary fins. It can be expected that the pneumatic spraying method will be widely used in the production of compact and efficient heat exchangers.

2 Spiral baffle

In shell and tube heat exchangers, the shell side is usually a weak link. The usual bow-shaped baffles can create a tortuous flow path system (zigzag flow path), which leads to large dead angles and relatively high backmixing. And these dead corners can cause the shell side fouling to intensify, which is detrimental to the heat transfer efficiency. Back mixing can also distort and reduce the mean temperature difference. The consequence of this is that arcuate baffles reduce the net heat transfer compared to plug flow.

Superior bow baffle shell-and-tube heat exchangers are difficult to meet the requirements of high thermal efficiency, so they are often replaced by other types of heat exchangers (such as compact plate heat exchangers). The improvement of the geometry of the ordinary baffle is the first step in the development of the shell process. Despite the introduction of sealing strips and additions such as deflection baffles and other measures taken to improve the performance of the heat exchanger, the major disadvantages of the conventional baffle design remain. To this end, the United States has proposed a new scheme, that is, the proposal

Spiral baffles are used. The advanced nature of this design has been confirmed by the results of fluid dynamics studies and heat transfer tests, and this design has been patented. This construction overcomes the major disadvantages of conventional baffles.

The design principle of the spiral baffle is very simple: the special plate with circular cross-section is installed in the "quasi-spiral baffle system". Each baffle plate accounts for 1/4 of the cross-section in the shell side of the heat exchanger, and its inclination is towards the axis of the heat exchanger, that is, it maintains an inclination with the axis of the heat exchanger. The peripheries of the adjacent baffles are connected and form a continuous spiral with the outer circle. The axial overlap of the baffles, to reduce the span of the support tube, can also be obtained in a double helix design. The helical baffle structure can satisfy a relatively wide range of process conditions. This design has great flexibility, can be for different operating conditions, select the best helix angle; respectively, the choice of overlapping baffle or double helix baffle structure.

3 twist tube

The Swedish company alares has developed a flat tube heat exchanger, usually called a twist tube heat exchanger. The Brown Company in Houston, USA, has made improvements. The manufacturing process of spiral flat tube includes two processes of "flattening" and "hot twisting. The improved twist tube heat exchanger is as simple as the traditional shell and tube heat exchanger, but there are many exciting advances. It has obtained the following technical and economic benefits: improved heat transfer, reduced fouling, real counterflow, reduced cost, no vibration, space saving, and no baffle elements.

Due to the unique structure of the tube, the tube side and the shell side are in spiral motion at the same time, which promotes the degree of turbulence. The overall heat transfer coefficient of the heat exchanger is 40% higher than that of the regular heat exchanger, while the pressure drop is almost equal. When assembling the heat exchanger, the spiral flat tube and the light tube can also be mixed. The heat exchanger is manufactured in strict accordance with ASME standards.

Where shell and tube heat exchangers and traditional devices can be replaced by such heat exchangers. It can obtain the best value obtained by ordinary shell and tube heat exchanger and plate and frame heat transfer equipment. It is estimated that it has broad application prospects in the chemical and petrochemical industries.

4 Spiral tube type

Spiral tube heat exchanger (TA) with wire wound on the tube as ribs (fins) is generally fixed on the tube by welding. However, this method has a series of effects on the quality of the entire equipment, because the brazing method must "deduct" a large part of the surface of the tube and wire from the heat exchange. More importantly, due to the rapid aging and crushing of the solder, the machine and equipment will be blocked, and the loss will be reported in advance.

5 Variable sound velocity pressurization

The variable sound velocity supercharged heat exchanger is a two-phase flow jet heat exchanger, which is widely used in various fields of steam-water heat exchange. Independent research and development by China Luoyang Blue Ocean Industrial Co., Ltd. It uses steam as the power, through the compression and mixing of steam and water, the water temperature rises instantaneously, and the pressure shock wave technology is used to achieve the effect of no external force supercharging. The significant energy saving and supercharging characteristics greatly reduce the user's cost and can replace the traditional heat exchanger.

The variable sound velocity booster heat exchanger is a hybrid steam-water heat exchange equipment. The steam is introduced into the mixing chamber in a jet state after adiabatic expansion technology and is uniformly mixed with the heated water after membrane treatment under the action of steam impact force to form a compressed mixture of steam and water with a certain calculated volume ratio. When the instantaneous compression density reaches a certain value, a two-phase fluid field phenomenon is formed. Under the excitation of the field state, the sound velocity value of the mixture has a transitional transition of breaking through the critical sound barrier, and a large number of pressure shock waves erupt at the same time. The unidirectional conduction characteristics of the pressure shock wave make the hot water reaching the design temperature instantaneously appear the phenomenon of pressure rise but no backflow in the constant cross-section pipe. The variable sound velocity booster heat exchange technology is based on the orderly intensification of the two-phase fluid field to force the completion of the "instantaneous heat transfer without external force supercharging" double effect.

1 Corrosion Protection

The application of heat exchanger in the oil refining industry is very extensive, its importance is also obvious, the utilization rate of heat exchange equipment directly affects the efficiency of the refining process and the cost of the cost. According to statistics, the heat exchanger accounts for about 1/5 of the investment in chemical construction, therefore, the utilization rate and life of the heat exchanger is an important issue worthy of study. From the point of view of the damage of the heat exchanger, corrosion is a very important reason, and the corrosion of the heat exchanger is a large number of widespread, can solve the problem of corrosion, is equal to solve the fundamental damage of the heat exchanger. In order to prevent the corrosion of the heat exchanger, it is necessary to find out the root causes of corrosion. The causes of corrosion of the heat exchanger are discussed from the following aspects.

A Corrosion

1. The decisive factor in the choice of material used for heat exchanger is its economy. The pipe materials include stainless steel, copper-nickel alloy, nickel-based alloy, titanium and zirconium, etc. In addition to the situation that welded pipes cannot be used in industry, welded pipes are used. Corrosion-resistant materials are only used in the tube side, and the shell side material is carbon steel.

2. Metal corrosion of heat exchanger

The principle of 2.1 metal corrosion metal corrosion refers to the chemical or electrochemical action of the surrounding medium, and often in and physical, mechanical or biological factors under the joint action of metal damage, that is, the metal in its environment under the action of the damage.

Several Common Types of Corrosion Damage of 2.2 Heat Exchanger

2.2.1 Uniform corrosion occurs on the entire surface exposed to the medium, or on a large area, and macroscopically uniform corrosion damage is called uniform corrosion.

2.2.2 Contact corrosion Two metals or alloys with different potentials are in contact with each other and immersed in the electrolyte solution, and there is current passing between them. The corrosion rate of metals with positive potential decreases and that of metals with negative potential increases.

2.2.3 Selective Corrosion The phenomenon that an element in the alloy preferentially enters the medium due to corrosion is called selective corrosion.

2.2.4 Pore corrosion is concentrated on individual small points on the metal surface. The corrosion with larger depth is called pitting corrosion, or pitting corrosion.

2.2.5 Crevice corrosion Severe crevice corrosion occurs in crevices and covered parts of the metal surface.

2.2.6 Erosion corrosion Erosion corrosion is a kind of corrosion that accelerates the corrosion process due to the relative movement between the medium and the metal surface.

2.2.7 Intergranular corrosion Intergranular corrosion is a kind of corrosion that preferentially corrodes the grain boundary and the area near the grain boundary of the metal or alloy, while the grain itself is relatively small.

2.2.8 Stress corrosion cracking (SCC) and corrosion fatigue SCC is a material fracture caused by the joint action of corrosion and tensile stress in a certain metal-medium system.

2.2.9 hydrogen damage metal in the electrolyte solution, due to corrosion, pickling, cathodic protection or electroplating, can produce damage caused by hydrogen seepage.

3. The effect of cooling medium on metal corrosion The most used cooling medium in industry is various natural water. There are many factors that affect metal corrosion, the main factors and their influence on several commonly used metals:

3.1 Dissolved Oxygen Dissolved oxygen in water is an oxidant participating in the cathodic process, so it generally promotes corrosion. When the concentration of oxygen in the water is not uniform, a concentration cell of oxygen will be formed, causing local corrosion. For carbon steel, low alloy steel, copper alloy and some grades of stainless steel, molten oxygen is the most important factor affecting their corrosion behavior in water.

3.2 other dissolved gases in the absence of oxygen in water, CO2 will cause corrosion of copper and steel, but will not promote corrosion of aluminum. Trace amounts of ammonia corrode copper alloys, but have no effect on aluminum and steel. H2S promotes corrosion of copper and steel, but has no effect on aluminum. SO2 reduces the pH of the water and increases the corrosion of the water to the metal.

3.3 Hardness In general, increased hardness of fresh water reduces corrosion of metals such as copper, zinc, lead, and steel. Very soft water is very corrosive, in this water, should not use copper, lead, zinc. In contrast, lead is resistant to corrosion in soft water and causes pitting corrosion in water with high hardness.

The corrosion of 3.4 pH steel in water with pH>11 is small, and the corrosion increases when pH<7.

Effect of 3.5 ions Chloride ions can damage the surface of passivated metals such as stainless steel and induce pitting or SCC.

Effect of 3.6 Scale CaCO3 Scale in Fresh Water. The CaCO3 scale layer is detrimental to heat transfer, but is beneficial to prevent corrosion.

4. The effect of heat transfer process on corrosion The corrosion behavior of metals is different under the condition of heat transfer and without heat transfer. In general, heat transfer exacerbates the corrosion of metals, especially under conditions of boiling, vaporization or overheating. In different media, or for different metals, the effect of heat transfer is not the same.

5. Anti-corrosion methods know the causes of various corrosion of heat exchangers, and reasonable selection of anti-corrosion measures can achieve the purpose of efficient use of equipment.

B Protection

In view of the corrosion situation discussed above, the following anti-corrosion methods are proposed: Here mainly introduces the corrosion inhibitor, electrochemical protection.

Corrosion inhibitor-chromate as the main component of the corrosion inhibitor is commonly used in cooling water system, chromate ion is an anode (process) inhibitor, when it is combined with the appropriate cathode inhibitor, can get a satisfactory and economic anti-corrosion effect. Chromate-zinc-polyphosphate: The use of polyphosphate is due to its ability to clean the metal surface and has corrosion inhibition. Polyphosphate can be partially converted into orthophosphate, and they can also form large colloidal cations with calcium to inhibit the cathodic process.

Chromate-zinc-phosphonate: This method uses sodium phosphonate instead of polyphosphate. Similar to the previous method, the carbamate phosphate can also be used in situations where the pH value is higher than that specified for the polyphosphate. The carbamyl phosphonate prevents scale and controls the precipitation of calcium salts even at a pH of 9.

Chromate-zinc-hydrolyzed polyacrylamide: Due to the dispersion of cationic copolymer hydrolyzed polyacrylamide, it can prevent or inhibit the generation of scale into dirt.

② Electrochemical protection-cathodic protection and anodic protection. Cathodic protection is the use of external DC power supply, so that the metal surface into a cathode to achieve protection, this method consumes a lot of electricity, high cost. Anodic protection is to connect the protected heat exchanger to the anode of the external power supply, so that the metal surface generates a passivation film to be protected.

7F Cleaning

For a long time, traditional cleaning methods such as mechanical methods (scraping, brushing), high-pressure water, chemical cleaning (pickling), etc. have caused many problems when cleaning heat exchangers: deposits such as scale cannot be completely removed, acid causes corrosion to equipment to form loopholes, residual acid causes secondary corrosion to materials or corrosion under scale, which eventually leads to replacement of equipment. In addition, cleaning waste liquid is toxic and requires a large amount of funds for wastewater treatment. The newly developed non-corrosive cleaning agent for the equipment, among which there should be a good technical agent, which is highly efficient, environmentally friendly, safe and non-corrosive, not only has good cleaning effect but also has no corrosion to the equipment, which can ensure the long-term use of the heat exchanger.

Cleaning agent (special adding wetting agent and penetrating agent, can effectively remove the most stubborn scale (calcium carbonate), rust, grease, slime and other sediments generated in the water equipment, and will not cause harm to human body, and will not cause erosion, pitting corrosion, oxidation and other harmful reactions to steel, copper, nickel, titanium, rubber, plastic, fiber, glass, ceramic and other materials, can greatly extend the service life of the equipment.

In the process of industrial production, sometimes due to the unexpected situation caused by improper operation of individual equipment or local pipeline fouling, blockage, affecting the normal operation of production. For this situation, it is mainly to quickly remove dirt to ensure the normal operation of the production device and restore the normal production state. Restore plant productivity.

For example, the scaling of chemical equipment causes the heat transfer coefficient of heat exchanger and other equipment to decrease, the flow area of the pipeline decreases or the flow resistance increases, so that the consumption of energy and materials increases, and the production efficiency decreases significantly. At this time, the production efficiency of the production equipment is restored by cleaning and descaling. Due to many reasons, heat exchanger equipment and pipeline lines will produce a lot of such as coking, oil dirt, scale, deposits, corrosion products, polymers, fungi, algae, slime and other dirt.

However, these dirt generated during work will cause equipment and pipeline lines to fail, and the device system will suffer from adverse conditions such as production decline, energy consumption and material consumption increase. When the dirt is particularly corrosive, the process will be interrupted, and the device system will be forced to stop production, which will directly cause various economic losses, and even malignant production accidents may occur. In today's scientific development, it is almost impossible to completely avoid the generation of dirt. Therefore, the cleaning of heat exchangers and other equipment has become an indispensable part of the production of industries (such as petroleum, chemical, electric power, and metallurgical industries).

High-pressure water jet cleaning heat exchanger is a physical cleaning method. Compared with traditional manual, mechanical cleaning and chemical cleaning, it has many advantages: low cleaning cost, good cleaning quality, fast cleaning speed, no environmental pollution, and no equipment corrosion.

China's high-pressure water jet cleaning technology is developing rapidly. The proportion of water jet industrial cleaning is close to 20% in large and medium-sized cities and enterprises, and it is growing at a rate of about 10% per year. It is estimated that 6-7 years, in China's industrial cleaning industry, high-pressure water jet cleaning technology will have an absolute advantage, is the only way for China's industrial cleaning.